ABSTRACTObjective. Latency of eye movements depends on cortical structures while speed of execution and accuracy depends mostly on subcortical brainstem structures. Prior studies reported in dyslexic reader children abnormalities of latencies of saccades (isolated and combined with vergence); such abnormalities were attributed to deficits of fixation control and of visual attention. In this study we examine speed and accuracy characteristics of horizontal eye movements in natural space (saccades, vergence and combined movements) in dyslexic reader children. Methods. Two paradigms are tested: gap paradigm (fixation offset 200 ms prior to target onset), producing shorter latencies, in both non-dyslexic reader and dyslexic reader children and simultaneous paradigm. Seventeen dyslexic reader children (mean age: 12 +/- 0.08 years) and thirteen non-dyslexic reader children (mean age: 12 +/- 1 years) were tested. Horizontal eye movements from both eyes were recorded simultaneously by a photoelectric device (Oculometer, Dr. Bouis). Results. For all movements tested (saccades, vergence, isolated or combined) and for both paradigms, the mean velocity and accuracy were similar in dyslexic readers and non-dyslexic readers; no significant difference was found. Conclusion. This negative but important result, suggests no dysfunction of brainstem ocular motor circuits in dyslexic readers. It contrasts results on latencies related to visual attention dysfunction at cortical level.

fig1: Spatial arrangement (a): LEDs were placed on an horizontal table at eye level. Three types of eye movements were elicited depending on the combination of the fixation and target LEDs: pure saccades far or close, pure vergence along the median axis, and combined movements; Temporal arrangement (b); schematic diagram of the temporal arrangement used in the two different paradigms (gap and simultaneous).

Mentions:
The spatial and the temporal arrangement are the same to that used in our previous study [15]. Briefly, eight LEDs were embedded in two isovergence circles at different distance (20 and 150 cm) on an horizontal table (see Figure 1(a)). Five LEDs were placed 150 cm from the subjects' eyes, one at the center, two at ±10°, and two at ±20°. The required mean angle of vergence for fixating these diodes was 2.3°. The other three LEDs were placed at a distance of 20 cm, one at the center and two at ±20°; the mean angle of vergence was 17.1°. Three types of movements were elicited: pure saccades, pure vergence, and combined movements. The fixation point was either the central LED at the distance of 20 cm or the central LED at the distance of 150 cm. Pure saccades to the left or to the right were elicited either at a close distance of 20 cm or at a far distance of 150 cm. Pure vergence was either convergence or divergence between the two LEDs placed on the median plane at 20 cm and 150 cm. Combined eye movements involved changes both in direction and in depth. The required saccade amplitude was always 20° for both pure saccades and combined movements. The required vergence movement was always 14.8° (17.1 − 2.3°) for both pure vergence along the median plane and combined eye movements.

fig1: Spatial arrangement (a): LEDs were placed on an horizontal table at eye level. Three types of eye movements were elicited depending on the combination of the fixation and target LEDs: pure saccades far or close, pure vergence along the median axis, and combined movements; Temporal arrangement (b); schematic diagram of the temporal arrangement used in the two different paradigms (gap and simultaneous).

Mentions:
The spatial and the temporal arrangement are the same to that used in our previous study [15]. Briefly, eight LEDs were embedded in two isovergence circles at different distance (20 and 150 cm) on an horizontal table (see Figure 1(a)). Five LEDs were placed 150 cm from the subjects' eyes, one at the center, two at ±10°, and two at ±20°. The required mean angle of vergence for fixating these diodes was 2.3°. The other three LEDs were placed at a distance of 20 cm, one at the center and two at ±20°; the mean angle of vergence was 17.1°. Three types of movements were elicited: pure saccades, pure vergence, and combined movements. The fixation point was either the central LED at the distance of 20 cm or the central LED at the distance of 150 cm. Pure saccades to the left or to the right were elicited either at a close distance of 20 cm or at a far distance of 150 cm. Pure vergence was either convergence or divergence between the two LEDs placed on the median plane at 20 cm and 150 cm. Combined eye movements involved changes both in direction and in depth. The required saccade amplitude was always 20° for both pure saccades and combined movements. The required vergence movement was always 14.8° (17.1 − 2.3°) for both pure vergence along the median plane and combined eye movements.

ABSTRACTObjective. Latency of eye movements depends on cortical structures while speed of execution and accuracy depends mostly on subcortical brainstem structures. Prior studies reported in dyslexic reader children abnormalities of latencies of saccades (isolated and combined with vergence); such abnormalities were attributed to deficits of fixation control and of visual attention. In this study we examine speed and accuracy characteristics of horizontal eye movements in natural space (saccades, vergence and combined movements) in dyslexic reader children. Methods. Two paradigms are tested: gap paradigm (fixation offset 200 ms prior to target onset), producing shorter latencies, in both non-dyslexic reader and dyslexic reader children and simultaneous paradigm. Seventeen dyslexic reader children (mean age: 12 +/- 0.08 years) and thirteen non-dyslexic reader children (mean age: 12 +/- 1 years) were tested. Horizontal eye movements from both eyes were recorded simultaneously by a photoelectric device (Oculometer, Dr. Bouis). Results. For all movements tested (saccades, vergence, isolated or combined) and for both paradigms, the mean velocity and accuracy were similar in dyslexic readers and non-dyslexic readers; no significant difference was found. Conclusion. This negative but important result, suggests no dysfunction of brainstem ocular motor circuits in dyslexic readers. It contrasts results on latencies related to visual attention dysfunction at cortical level.